1. Field of the Invention
The present invention relates to a hand-held instrument for reflection measuring optical density and colour on printed sheets.
2. Description of the Prior Art
Instruments of this type are used in the printing industry in the form of colour measuring instruments and top colour illumination densitometers for controlling the colour flow in printing machines, particularly in multicolour screen printing.
Densitometers and colour measuring instruments of this type are known, for example, from European Patent 0 299 445 and German Patent 43 18 637. The essential components of instruments of this type are the housing, a display field for displaying the measured values, operating elements in the form of switches and keys, an electronic control unit arranged within the housing and a measuring head containing all mechanical and optical components required for recording the measured value. Components of this type, in addition, individually, have been described in closer detail in German Patent Application 43 05 968 (corresponding to U.S. Pat. No. 5,373,364). Instruments of the afore-described type increasingly are used in connection with computers in such a way that the measured values are transmitted to the computer and are further evaluated with the aid of software programs to be graphically displayed on the screen. The computer is operated by a keyboard and, increasingly, by additional input devices.
The two most commonly used input devices are those which are designated by the technical language mouse and trackball. Mouse and trackball are connected to the computer by means of a cable. However, a few types thereof also communicate with the computer by infra-red pulses or high-frequency radio signals. Essentially, mouse and trackball comprise a ball which, by moving it, can position a cursor at any desired point of the computer screen. In addition, mouse and trackball are provided with one or more click knobs conveying function commands to the computer. Mouse and trackball are distinguished from one another by a different arrangement of the ball on the housing. Concerning the mouse, the ball is arranged on the bottom side thereof and is moved on the tabletop by shifting the mouse, whereas in the trackball the ball is arranged on the upper side and can be moved in all directions by the operator's finger. Both input devices operate in such a way that the movement of the ball is transmitted to two optoelectronic elements transmitting the required displacment signals for the cursor in the X and Y directions to the screen.
The principle of operation of an electromechanically operating converter element converting a rotary movement to electric signals is described in German Patent Application 24 56 541 according to which the rotary movement of one or two wheels arranged at the bottom side on the converter element is transferred to a slotted aperture to which light is applied and is transmitted by a light pulse to a photocell.
According to a special design of the trackball, the ball is replaced by a rocking switch tiltable in all directions. Ball and rocking switch have equivalent functions so that the following description applies to both types even if no express reference is any longer made thereto. In connection with special software programs mouse and trackball contribute to a sustantially simplifying and expediting the operation of the computer, with the functional fields being displayed on the screen the functions of which can be easily recognized by the operator by letters or symbols. As soon as the cursor has been positioned in the desired functional field with the aid of the ball, the function as displayed can be performed by one of the click knobs. However, the operating comfort provided by mouse and trackball is substantially restricted if it is also to be used for measurements of the afore-mentioned type as in that case, in addition to the input device also the hand-held measuring instrument is to be used, i.e. both instruments will have to be alternatingly taken into the operator's hand.